In this chapter we will help you understand the
UnitOfWork. A Unit of Work is similar to an
object-level transaction. A new Unit of Work is implicitly started
when a DocumentManager is initially created or after
DocumentManager#flush() has been invoked. A Unit of Work is
committed (and a new one started) by invoking
A Unit of Work can be manually closed by calling
DocumentManager#close(). Any changes to objects within this
Unit of Work that have not yet been persisted are lost.
The size of a Unit of Work mainly refers to the number of managed documents at a particular point in time.
How costly a flush operation is in terms of performance mainly depends on the size. You can get the size of your Unit of Work as follows:
The size represents the number of managed documents in the Unit of Work. This size affects the performance of flush() operations due to change tracking and, of course, memory consumption, so you may want to check it from time to time during development.
Do not invoke
flush after every change to a
document or every single invocation of persist/remove/merge/...
This is an anti-pattern and unnecessarily reduces the performance
of your application. Instead, form units of work that operate on
your objects and call
flush when you are done. While serving a
single HTTP request there should be usually no need for invoking
flush more than 0-2 times.
You can get direct access to the Unit of Work by calling
DocumentManager#getUnitOfWork(). This will return the
UnitOfWork instance the DocumentManager is currently using.
Directly manipulating a UnitOfWork is not recommended. When working directly with the UnitOfWork API, respect methods marked as INTERNAL by not using them and carefully read the API documentation.
A document can be made persistent by passing it to the
DocumentManager#persist($document) method. By applying the
persist operation on some document, that document becomes MANAGED,
which means that its persistence is from now on managed by an
DocumentManager. As a result the persistent state of such a
document will subsequently be properly synchronized with the
DocumentManager#flush() is invoked.
persist method on a document does NOT
cause an immediate insert to be issued on the database. Doctrine
applies a strategy called "transactional write-behind", which means
that it will delay most operations until
DocumentManager#flush() is invoked which will then issue all
necessary queries to synchronize your objects with the database in
the most efficient way.
The document identifier is generated during
persist if not previously
specified. Users cannot rely on a document identifier being available during
The semantics of the persist operation, applied on a document X, are as follows:
- If X is a new document, it becomes managed. The document X will be entered into the database as a result of the flush operation.
- If X is a preexisting managed document, it is ignored by the persist operation. However, the persist operation is cascaded to documents referenced by X, if the relationships from X to these other documents are mapped with cascade=PERSIST or cascade=ALL.
- If X is a removed document, it becomes managed.
- If X is a detached document, the behavior is undefined.
Do not pass detached documents to the persist operation.
When committing your documents you can specify an array of options to the
flush method. With it you can send options to the underlying database
You can configure the default flush options on your
if you want to set them globally for all flushes.
Safe is set to true by default for all writes when using the ODM.
A document can be removed from persistent storage by passing it to
DocumentManager#remove($document) method. By applying the
remove operation on some document, that document becomes
REMOVED, which means that its persistent state will be deleted once
DocumentManager#flush() is invoked. The in-memory state of a
document is unaffected by the
remove on a
document does NOT cause an immediate query to be issued on the
database. The document will be removed on the next invocation of
DocumentManager#flush() that involves that document.
The semantics of the remove operation, applied to a document X are as follows:
- If X is a new document, it is ignored by the remove operation. However, the remove operation is cascaded to documents referenced by X, if the relationship from X to these other documents is mapped with cascade=REMOVE or cascade=ALL.
- If X is a managed document, the remove operation causes it to become removed. The remove operation is cascaded to documents referenced by X, if the relationships from X to these other documents is mapped with cascade=REMOVE or cascade=ALL.
- If X is a detached document, an InvalidArgumentException will be thrown.
- If X is a removed document, it is ignored by the remove operation.
- A removed document X will be removed from the database as a result of the flush operation.
A document is detached from a DocumentManager and thus no longer
managed by invoking the
method on it or by cascading the detach operation to it. Changes
made to the detached document, if any (including removal of the
document), will not be synchronized to the database after the
document has been detached.
Doctrine will not hold on to any references to a detached document.
The semantics of the detach operation, applied to a document X are as follows:
- If X is a managed document, the detach operation causes it to become detached. The detach operation is cascaded to documents referenced by X, if the relationships from X to these other documents is mapped with cascade=DETACH or cascade=ALL. Documents which previously referenced X will continue to reference X.
- If X is a new or detached document, it is ignored by the detach operation.
- If X is a removed document, the detach operation is cascaded to documents referenced by X, if the relationships from X to these other documents is mapped with cascade=DETACH or cascade=ALL/Documents which previously referenced X will continue to reference X.
There are several situations in which a document is detached
automatically without invoking the
DocumentManager#clear()is invoked, all documents that are currently managed by the DocumentManager instance become detached.
- When serializing a document. The document retrieved upon subsequent unserialization will be detached (This is the case for all documents that are serialized and stored in some cache).
detach operation is usually not as frequently needed and
Merging documents refers to the merging of (usually detached)
documents into the context of a DocumentManager so that they
become managed again. To merge the state of a document into an
DocumentManager use the
method. The state of the passed document will be merged into a
managed copy of this document and this copy will subsequently be
1 // some detached document $document = $dm->merge($detachedDocument); // $document now refers to the fully managed copy returned by the merge operation. // The DocumentManager $dm now manages the persistence of $document as usual. The semantics of the merge operation, applied to a document X, are as follows:$detachedDocument = unserialize($serializedDocument); 2 3 4 5 6 7 8 9
- If X is a detached document, the state of X is copied onto a pre-existing managed document instance X' of the same iddocument or a new managed copy X' of X is created.
- If X is a new document instance, an InvalidArgumentException will be thrown.
- If X is a removed document instance, an InvalidArgumentException will be thrown.
- If X is a managed document, it is ignored by the merge operation, however, the merge operation is cascaded to documents referenced by relationships from X if these relationships have been mapped with the cascade element value MERGE or ALL.
- For all documents Y referenced by relationships from X having the cascade element value MERGE or ALL, Y is merged recursively as Y'. For all such Y referenced by X, X' is set to reference Y'. (Note that if X is managed then X is the same object as X'.)
- If X is a document merged to X', with a reference to another document Y, where cascade=MERGE or cascade=ALL is not specified, then navigation of the same association from X' yields a reference to a managed object Y' with the same persistent iddocument as Y.
merge operation is usually not as frequently needed and
remove. The most common scenario for
merge operation is to reattach documents to an
DocumentManager that come from some cache (and are therefore
detached) and you want to modify and persist such a document.
If you load some detached documents from a cache and you
do not need to persist or delete them or otherwise make use of them
without the need for persistence services there is no need to use
merge. I.e. you can simply pass detached objects from a cache
directly to the view.
References between documents and embedded documents are represented just like in regular object-oriented PHP, with references to other objects or collections of objects.
Establishing a reference to another document is straight forward:
Here is an example where we add a new comment to an article:
Or you can set a single reference:
Removing an association between two documents is similarly straight-forward. There are two strategies to do so, by key and by element. Here are some examples:
Or you can remove a single reference:
When working with collections, keep in mind that a Collection is
essentially an ordered map (just like a PHP array). That is why the
remove operation accepts an index/key.
removeElement is a
separate method that has O(n) complexity, where n is the size of
Persisting, removing, detaching and merging individual documents can become pretty cumbersome, especially when a larger object graph with collections is involved. Therefore Doctrine provides a mechanism for transitive persistence through cascading of these operations. Each reference to another document or a collection of documents can be configured to automatically cascade certain operations. By default, no operations are cascaded.
The following cascade options exist:
- persist : Cascades persist operations to the associated documents.
- remove : Cascades remove operations to the associated documents.
- merge : Cascades merge operations to the associated documents.
- detach : Cascades detach operations to the associated documents.
- all : Cascades persist, remove, merge and detach operations to associated documents.
The following example shows an association to a number of addresses. If persist() or remove() is invoked on any User document, it will be cascaded to all associated Address documents in the $addresses collection.
Even though automatic cascading is convenient it should be used with care. Do not blindly apply cascade=all to all associations as it will unnecessarily degrade the performance of your application.
Doctrine provides the following ways, in increasing level of power and flexibility, to query for persistent objects. You should always start with the simplest one that suits your needs.
The most basic way to query for a persistent object is by its
identifier / primary key using the
DocumentManager#find($documentName, $id) method. Here is an
The return value is either the found document instance or null if no instance could be found with the given identifier.
DocumentManager#find() is just a shortcut for the
DocumentManager#getRepository($documentName) returns a
repository object which provides many ways to retrieve documents of
the specified type. By default, the repository instance is of type
Doctrine\ODM\MongoDB\DocumentRepository. You can also use
custom repository classes.
To query for one or more documents based on several conditions that
form a logical conjunction, use the
methods on a repository as follows:
1 // All users that are 20 years old $users = $dm->getRepository('User')->findBy(array('age' => 20)); // All users that are 20 years old and have a surname of 'Miller' $users = $dm->getRepository('User')->findBy(array('age' => 20, 'surname' => 'Miller')); // A single user by its nickname $user = $dm->getRepository('User')->findOneBy(array('nickname' => 'romanb')); 2 3 4 5 6 7 8 9 10
You can learn more about Repositories in a dedicated chapter.
Whenever you have a managed document instance at hand, you can traverse and use any associations of that document as if they were in-memory already. Doctrine will automatically load the associated objects on demand through the concept of lazy-loading.
The most powerful and flexible method to query for persistent objects is the Query\Builder object. The Query\Builder object enables you to query for persistent objects with a fluent object oriented interface.
You can create a query using
DocumentManager#createQueryBuilder($documentName = null). Here is a
To query documents with a ReferenceOne association to another document, use the
To find documents with a ReferenceMany association that includes a certain document, use the